AMATEUR BASIC LICENCE COURSE - LESSON OUTLINE - MAR 1998
Numbers in [ ] are chapters from the RAC study guide.
Items marked * are extra material, not on the exam.
Each numbered item should take approximately 15 minutes to
present. Each session is 3 hours (12 items, including a 15
minute break.)
E. WEEK 3 - MORNING - Antennas
INSTRUCTOR: Grant VE3GCQ
EQUIPMENT: antenna tuner, SWR meter
1. Homework review
2. MORSE LESSON 5: ZVXJ
Words JAZZ VEX ZOOM JUST SIX VOW
3. Transmission Lines [7]
a) You need two wires to connect a battery to a load.
Likewise, you need two conductors to connect a transmitter
to an antenna.
b) This is called a "transmission line": two conductors
designed to carry RF energy efficiently.
There are two types.
c) BALANCED or "parallel" transmission line has two identical
wires side by side, with nothing around them. They have
some insulator between them to keep them evenly spaced.
(SHOW EXAMPLE OF TWIN-LEAD)
d) Balanced lines are not shielded, and must be kept away from
other conductors like metal towers or the ground.
e) UNBALANCED or "coaxial" transmission line has one conductor
inside the other. The inner conductor is a wire, the outer
conductor is a hollow tube. This tube can be solid copper
or braided wire. (SHOW EXAMPLES OF COAX).
f) The outer conductor is a shield -- all RF energy stays
within it. Coaxial cable can be freely placed near metal or
even buried, which is why it is commonly used.
g) All transmission lines have a CHARACTERISTIC IMPEDANCE.
If you were to connect a battery to an infinitely long line,
it will accept current only at a certain rate. It looks
like a resistor.
h) The characteristic impedance is measured in ohms. It is
determined by physical diameter and spacing of the
conductors, and the dielectric material (insulator) between
them.
i) TV "twin-lead" has a characteristic impedance of 300 ohms.
j) Coaxial cable used for television has a characteristic
impedance of 75 ohms.
k) Coaxial cable used for most amateur, CB, and commercial
radio has a characteristic impedance of about 50 ohms.
l) The characteristic impedance is NOT affected by the length
of the line. For example, a piece of RG-213 cable has a
characteristic impedance of 50 ohms, whether it's 1 foot
long or 100 feet long.
m) PRACTICE QUESTIONS: 2-118, 2-083, 2-082, 2-014.
4. Impedance Matching [7]
a) Every antenna has a natural impedance.
Transmitters are designed to drive a certain impedance
(usually 50 ohms).
For optimum power transfer, the antenna impedance must match
the transmitter, and the line impedance must match both.
b) It's easy to make the line impedance match the transmitter
-- just buy the right cable. (50 ohm cable for amateur use.)
c) The problem is making the antenna match. If the antenna
impedance is different from the line, power is reflected
back from the antenna. This causes power to be lost (turned
to heat) in the transmission line.
d) If the antenna impedance doesn't match the transmitter, the
transmitter can overheat or be damaged.
e) The ideal is to "terminate the transmission line in its
characteristic impedance", that is, make the antenna match
the line perfectly. Then all power is absorbed by the load
(the antenna).
f) A perfect match looks exactly like an infinitely long
transmssion line.
g) One way to match the antenna is with a transformer. These
often match balanced antennas to unbalanced transmission
line, and so are called "baluns" (for BALanced/UNbalanced).
For example, you can buy a commercial balun to give a 4:1
impedance ratio (it will match 200 ohms to a 50 ohm line).
h) Another way to match impedances is with an "antenna tuner",
also called a "match box" or "transmatch". (SHOW TUNER)
This can prevent a transmitter mismatch (and thus prevent
transmitter damage). But it does not match the line to the
antenna, so power is still lost.
i) PRACTICE QUESTIONS: 2-081 (DISCUSS), 2-086, 2-121.
5. Standing Wave Ratio (SWR) [7]
a) When the line doesn't match the antenna, power is reflected.
This combines with the outgoing or "forward" power to cause
STANDING WAVES on the line.
b) Standing waves are measured by Standing Wave Ratio, or SWR.
A standing wave ratio of 1:1 is a perfect match.
c) As the mismatch gets worse, the standing wave ratio goes up.
Most transmitters can tolerate an SWR up to 2:1.
d) The worst possible match is a short circuit or an open
circuit (no antenna connected). In either of these cases,
the SWR becomes infinite.
e) Standing wave ratio is measured by an SWR meter.
1) The SWR meter reads forward and reflected power
(or sometimes forward and reflected voltage). (SHOW METER)
2) Most meters have a single meter and a switch. You set the
meter to read full scale in the "forward" position. Then
you switch to the reverse position, and the meter indicates
SWR directly.
f) PRACTICE QUESTIONS: 2-089, 2-090, 2-109.
6. Half-wave dipole [8]
a) The most basic antenna is a half-wave dipole.
b) A wire one-half wavelength long will resonate, like a guitar
string. When it resonates it transmits and receives radio
waves most efficiently.
c) For example, at 1 MHz the wavelength is 300 metres.
Therefore a dipole for 1 MHz would be 150 metres long, half
a wavelength.
d) Remember that shorter wavelengths correspond to higher
frequencies. So if you shorten a dipole, you make it
resonate at a higher frequency.
e) If you were to measure the AC CURRENT in the antenna, you
would find the maximum amplitude at the CENTER of the
antenna. You would find no current at the ends.
(SHOW DIAGRAM)
f) If you were to measure the AC VOLTAGE on the antenna, you
would find the maximum amplitude at the ENDS of the antenna.
You would find no voltage at the center.
g) For most dipoles, the transmission line is connected at the
center. This is the place of maximum current. This is
called "center feed".
h) A center-fed dipole has an impedance of about 73 ohms. This
is a good match to 75-ohm cable.
i) There is a variant called a folded dipole which has a feed
point impedance of about 300 ohms. (SHOW ILLUSTRATION)
j) Most of the RF energy is radiated broadside from a dipole.
No energy is radiated from the ends (i.e., along the length
of the dipole). (SHOW DIAGRAM)
k) The angle of radiation up from the horizon is determined by
how high the antenna is above ground. For best results,
mount dipoles at least 1/4 wavelength above ground.
l) Dipoles also work on odd multiples ("harmonics") of the
resonant frequency. For example, a 1 MHz dipole will also
work for 3, 5, 7 MHz and so on.
m) PRACTICE QUESTIONS: 2-008, 2-095, 2-015, 2-093.
7. BREAK
8. REGS: Power Limits
a) The maximum power you can use depends on the operating mode.
b) For most modes, you can measure the DC power supplied to the
final amplifier. This "DC input power" can be up to 250
watts.
c) Or, you can measure the actual RF output power from the
transmitter. This "carrier output power" can be up to 190
watts.
d) Single-sideband transmitters are measured in terms of "Peak
Envelope Power", also called "PEP output power". This can
be up to 560 watts. Since this is hard to measure, for
practical purposes you should buy a transmitter that is
rated lower than this.
e) Basic: 250 W DC input, 560 W PEP output, 190 W carrier out
f) If you have ADVANCED qualification, these limits go up to:
1000 watts DC input power
750 watts carrier output power
2250 watts PEP output power (for SSB transmitters)
g) You cannot own a transmitter capable of producing more than
twice your authorized power, even if you turn it down. On
the exam, this is stated "more than 3 decibels" over your
authorized power. (We'll learn about decibels later.)
h) For "radiotelephony" (voice) you must not use more than 100%
modulation. Your transmitter must either have a modulation
indicator, or an "ALC" circuit which automatically limits
the modulation to a legal value.
i) You must have a way to "determine" your transmitting
frequency. For most transmitters, this is the tuning dial.
j) When operating below 148 MHz, your transmitter's frequency
must be a stable as "crystal control." All modern
manufactured transmitters meet this requirement.
k) PRACTICE QUESTIONS: 3-021, 3-017, 3-024.
9. Vertical Antennas
a) If you take half of a dipole antenna and mount it vertically
over ground, you get a "quarter-wave vertical" antenna.
b) The electrical behavior of the ground can be simulated by a
"ground plane", thus known as a "ground plane" antenna.
The ground plane can be horizontal wires or flat metal (such
as the roof of your car).
c) This antenna is OMNIDIRECTIONAL, which means it radiates
equally well in all directions.
d) The feed point impedance of the 1/4 wave antenna is about 50
ohms, which is a good match to 50-ohm coaxial cable.
e) You can also make a vertical antenna which is 5/8 of a
wavelength long, thus called a "5/8-wave vertical".
Its main advantage is a lower angle of radiation, which
gives better range.
f) You can make an antenna physically shorter without changing
its resonant frequency, by adding LOADING COILS.
These are just inductors (coils) in series with the antenna
wire.
g) A series inductance makes the antenna element look
electrically longer.
h) This is used to make short antennas.
i) PRACTICE QUESTIONS: 2-018, 2-101, 2-114, 2-040.
10. Yagi antenna [8]
a) The Yagi-Uda antenna, or simply Yagi, is a DIRECTIONAL
antenna named after its inventors.
b) "Directional" means it concentrates radio energy in one
direction, and it is most sensitive in that direction.
c) It consists of a dipole, a REFLECTOR, and one or more
DIRECTORS. (SHOW BLOCK DIAGRAM)
d) The reflector is slightly longer than the dipole, and is
mounted "behind" the dipole. It tends to reflect radio
energy back the other way (hence the name).
e) The directors are slightly shorter than the dipole, and is
mounted "in front" of the dipole. Directors tend to focus
the radio energy.
f) The reflector and directors are just wires, not connected to
anything. They work by picking up RF radiated by the
dipole. So they are called "parasitic" elements. The
antenna is sometimes called a "parasitic array".
g) Since the dipole is the only thing connected to the
transmitter, it is called the "driven element."
h) PRACTICE QUESTIONS: 2-110, 2-111, 2-011.
11. Antenna specs: gain and bandwidth
a) The Yagi concentrates the RF energy in one direction. So,
10 watts into a Yagi may deliver as much signal to the far
end as 20 watts into a dipole.
b) In this case, we would say the Yagi has a "two times" power
gain over the dipole.
c) Except we don't say "two times" or "ten times". We measure
power gain in DECIBELS.
d) Decibels indicate a power ratio. The two easiest ones to
remember are:
3 decibels = two times the power
10 decibels = ten times the power
e) So if a Yagi has 10 decibels gain over a dipole, it appears
to put out 10 times as much power. 10 watts into this
antenna would be as effective as 100 watts into a dipole.
f) You're not really radiating more power, you're just focusing
it in one direction. So this doesn't affect your legal
limits.
g) Sometimes you'll hear about decibels over an ISOTROPIC
antenna. This is a hypothetical "point source" antenna
which radiates uniformly in all directions. So it's even
less focused than a dipole.
h) You'll also hear about antenna BANDWIDTH. This is the range
of frequencies for which the antenna will give an acceptable
SWR (typically 2:1).
i) For testing transmitters, we use a "dummy load". This is a
device which looks like an antenna, but doesn't radiate any
RF signal.
j) PRACTICE QUESTIONS: 2-113, 2-106.
12. Polarization [8]
a) Remember that a radio wave has an electric "E" field, and a
magnetic "M" field, at right angles. So if one is
oscillating vertically, the other is oscillating
horizontally.
b) We call the direction of the electric field the POLARIZATION
of the radio wave.
c) Two radio stations must use the same polarization in order
to communicate.
d) This is most important for line-of-sight communications,
such as VHF radio. For instance, all 2m FM communications
is done with vertical polarization.
e) This is less important for skywave communications on HF,
because reflection from the ionosphere will change the
polarization of the signal.
f) PRACTICE QUESTIONS: 2-007, 2-116.
13. MORSE REVIEW 5: ZVXJ
Words VIEW BOX JUNK FIZZ UVULA JOG ZING XEROX
JAZZ VEX ZOOM JUST SIX VOW
F. WEEK 3 - AFTERNOON - The Amateur Station
INSTRUCTOR: VE3XOX
PROPS: SWR meter, dummy load, transmitter, antenna, power
supply
1. DEMO: how to use SWR meter and dummy load
a) Dummy antenna or "dummy load" is used to test or tune up
transmitters, without radiating a signal. [8]
1) Connect it (with coaxial cable) to the antenna socket on
your transmitter.
2) Be careful not to transmit for long periods, as the dummy
load will heat up. Check the rating of the dummy load.
3) Do NOT use a light bulb.
b) You know the SWR meter measures the antenna mismatch.
1) Connect it between the transmitter and the antenna. You
must connect it the right way 'round. One socket will be
labelled "transmitter", and the other "antenna".
2) Set up your transmitter to radiate a continuous signal
(CW, or FM, or unmodulated AM).
3) CALIBRATE the SWR meter. Select "forward," transmit a
signal, and turn the adjustment knob until the meter reads
full scale. (If you have separate meters, set the "forward"
meter to full scale.)
4) READ the SWR. Select "reverse", transmit a signal, and read
the SWR off the meter scale. (If you have separate meters,
read the "reverse" meter.)
5) Be sure to identify yourself after sending a test signal.
E.g., "VE3RHJ testing".
2. PRACTICAL: Safety [16]
(This material is also on the exam.)
Amateur equipment uses potentially lethal voltages.
So we have established several standard precautions to avoid
shock or electrocution.
a) Connect the chassis of equipment to earth ground.
If the wrong wire inside the equipment shorted to the metal
chassis, it could put several hundred volts on the OUTSIDE
of the equipment. Connecting the chassis to ground will
prevent this, and ensure that a fault will not put high
voltage on the metal chassis.
b) 3 wire power cords are often used to connect the chassis to
ground. The third wire is the ground wire.
Do NOT bypass this wire: it is an essential safety feature.
c) Do NOT service equipment while it is switched on!
You risk shock while the equipment is turned on.
d) In fact, UNPLUG equipment before servicing it!
Even when switched off, there are lethal voltages at some
places inside the unit.
e) If you ever come across someone who is being electrocuted,
DO NOT touch him. Turn off the high voltage first!
The human body is a conductor, so if you touch him, you'll
get shocked too.
f) PRACTICE QUESTIONS: 2-197, 1-007, 1-037.
3. MORSE LESSON 6: 12345
4. Power Supplies [10]
The purpose of a power supply is to convert AC, from the
wall socket, to DC at some desired voltage. On the block
diagram, there are six parts: (SHOW BLOCK DIAGRAM)
a) Input. This is the AC wall socket.
b) Transformer. Remember that a transformer can change AC from
one voltage to another. So, while we still have AC, we
change the voltage to the desired value.
c) Rectifier. This is a diode, which only lets current pass
one way. It blocks the "wrong" half-cycle of the sine wave,
thus it converts AC to pulsating DC.
d) Filter. This is often a capacitor, which can store and
release charge. It converts the pulsating DC to smooth DC.
e) Regulator. This REGULATES the DC, that is, holds it exactly
to the desired value. Even if the AC voltage changes, the
DC output will remain exact.
f) Output. This is the DC output to your rig. (SHOW EXAMPLE)
g) PRACTICE QUESTIONS: 1-001, 1-003, 1-044, 1-046.
5. Setting up an HF Station [11]
We'll first talk about what Industry Canada wants you to
know about the HF station components.
a) You know you need a TRANSMITTER, to generate radio signals.
b) You know you need a RECEIVER, to hear the other guy's radio
signals.
c) You also need a TRANSMIT/RECEIVE SWITCH. This lets your
transmitter and receiver share the same antenna. When you
switch from receive to transmit, it must do three things:
1) Disconnect the antenna from the receiver, and connect it to
the transmitter.
2) MUTE the receiver. Even with the antenna disconnected, your
receiver will pick up your transmitter. This basically
turns off the receiver while you're transmitting.
3) Turn on the transmitter.
d) Unless you collect antiques, you'll probably buy all three
of these in one package. This is called a TRANSCEIVER.
(SHOW HF STATION BLOCK DIAGRAM)
e) If you get your Advanced qualification, you might add a
LINEAR AMPLIFIER. This increases your transmitter power.
Since you don't always want to run maximum power, you'll
have some arrangement to bypass the linear amplifier. (This
is built into most modern "linears".)
f) Next you should have a LOW-PASS FILTER. This reduces
interference to TVs and radios. We'll talk about this
shortly.
g) You know what an SWR meter is. It's also called an SWR
BRIDGE, and goes AFTER the low-pass filter.
h) You'll probably want to use several of the HF bands, and
thus several antennas. So you'll want an ANTENNA SWITCH to
choose which antenna to use.
i) For the bands ABOVE 14 MHZ, the wavelength is short enough
that you can make Yagi antennas. Many of these antennas
include a matching device for a 50 ohm impedance, so they
can be connected directly to the transmitter.
j) BELOW 14 MHZ, you'll probably make long wire or dipole
antennas. Many of these will need an ANTENNA TUNER to
convert their impedance to 50 ohms. (SHOW TUNER)
k) Finally, your transmitter's final amplifier may need to be
tuned for your output frequency. It's best to tune it into
a DUMMY LOAD so that you don't radiate signals during
tune-up.
l) PRACTICE QUESTIONS: 2-171, 2-176, 2-217.
6. Setting up a 2m Station
Industry Canada doesn't have any questions specifically for
2m stations. So this is for your information.
a) You will need a 2m TRANSCEIVER. This can be either a
handheld radio (SHOW EXAMPLE), a mobile radio designed for a
car, or a base station designed for the home.
b) Many people use mobile radios at home. Mobile radios run on
12 volts DC, so you need a POWER SUPPLY which plugs into the
wall and produces 12 volt DC.
c) You can buy LINEAR AMPLIFIERs for 2m, but you probably won't
need one.
d) Since the 2m transceiver works on a single band, you'll
probably only need a single antenna. The most common are:
1) 1/4 wave or 5/8 wave vertical antenna. These are simple and
inexpensive, and can attach magnetically on the roof of your
car. For home use you'll probably need radials.
2) J-pole. This is a vertical antenna which doesn't require
radials. It's good for home use.
3) Yagi. To increase your range you need a directional antenna
with gain, and an antenna rotator to point it. 2m Yagis up
to 11 elements are reasonably small and can be turned with a
TV antenna rotator.
e) You probably only need to borrow an SWR bridge when you're
installing your antenna. After that, the SWR shouldn't
change too much.
7. Setting up a Digital Station [11]
There are three basic digital modes: packet radio,
radioteletype, and AMTOR. We'll learn more about how they
work when we discuss transmitters. The basic station layout
is the same for all three, and this might be on the exam:
a) INPUT/OUTPUT on the block diagram refers to the keyboard and
screen of your computer.
b) The COMPUTER converts what you type to digital signals, and
displays received digital signals on the screen.
c) The MODEM is the heart of the system. It converts digital
signals to audio signals (sounds), which an ordinary radio
can send and receive.
d) For packet radio, you'll also hear the modem called a "TNC"
(Terminal Node Controller).
e) Packet radio uses the "ASCII" encoding for typed characters.
And it adds routing and control information using the
"AX.25" protocol. Remember the names.
f) Finally, you have an ordinary TRANSCEIVER,
g) And an ordinary ANTENNA. Nothing special here.
h) PRACTICE QUESTIONS: 3-001, 3-003, 3-005.
8. BREAK
9. REGS: Operating Procedures [12]
This is what Industry Canada requires you to know:
a) The first rule of all amateur communication: listen before
you transmit! (Yes, this is on the exam.)
b) When you are talking on the radio, you must identify your
station on your FIRST transmission, on your LAST
transmission, and at least every 30 minutes in between. You
identify by announcing your callsign by voice or morse code.
c) You are NOT required to keep a logbook of all your
transmissions. But many amateurs do. (SHOW LOGBOOK) It's
especially nice if you want to confirm contacts with DX
stations.
d) You must yield the frequency for emergency transmisions.
There are three levels of emergency:
1) DISTRESS. This has the highest priority. An airplane is in
distress when its engine quits.
2) URGENCY. This has the second highest priority. For
example, an airplane would send Urgency transmissions if it
had only 15 minutes' fuel left.
3) SAFETY. This is the third highest priority. An airplane
would send this if it was lost.
4) You should remember this order: first Distress, then
Urgency, then Safety.
e) If you hear a distress call:
1) Don't jump in; wait to see if someone else has answered it.
2) If no one has, you should render assistance.
3) This is the ONLY time you can knowingly interfere with
another station.
f) PRACTICE QUESTIONS: 3-013, 3-071, 3-085.
10. Radio Frequency Interference & TVI "not your transmitter"
We teach you about Radio Frequency Interference and
Television Interference for two reasons. First, there are a
lot of RFI and TVI questions on the exam. Second, it's your
responsibility as an amateur not to interfere with other
services, and if you have neighbors, you may run into this
someday.
a) Front-End Overload
This simply means that your signal is so powerful that it's
overloading the receiver circuits of your neighbor's TV.
It's common when you run high power on the HF bands.
1) Your transmitter is OK, so there's nothing you can fix
there.
2) You need to make the TV less sensitive to your HF
transmitter, without affecting its reception of VHF and UHF
TV signals. You do this by adding a HIGH PASS FILTER to the
TV's antenna input. This will pass the high frequencies
(VHF and UHF), but block the low frequencies.
b) Audio Rectification
It's also possible for your powerful signal to get into the
audio circuits, and get rectified (turned to audio). This
is common when the speaker wires of a stereo system pick up
your signal.
1) The clue: since it's overloading the AUDIO circuits, it will
appear wherever the TV/radio/stereo is tuned.
2) Again, your transmitter is OK.
3) You need to prevent your neighbor's audio circuits from
picking up RF. You do this by shielding his receiver,
and/or by putting filters on the speaker wiring.
c) Adjacent Channel interference
This is like front-end overload, but occurs when your
frequency is very close to the TV frequency. For example,
you may be transmitting on the 50 MHz band, and your
neighbor is trying to watch channel 2 at 54 MHz.
1) High-pass filters aren't good enough to separate these
signals.
2) You might be able to build a BAND REJECT FILTER to block
only your transmitting frequency.
3) But probably, you'll have to come to an accomodation with
your neighbor. Reduce your power output, or only operate
during certain hours.
d) PRACTICE QUESTIONS: 2-192, 2-194, 2-195, 2-257.
11. RFI and TVI "your transmitter"
a) Harmonics
This is a case where your neighbor's TV is ok, but your
transmitter is the problem. You're actually radiating in
the television band. It happens like so:
1) If your RF isn't an absolutely perfect sine wave, it will
contain HARMONICS. These are integer multiples of your base
(fundamental) frequency. For example, if you're
transmitting on 7 MHz, the "second harmonic" is 14 MHz, the
"third harmonic" is 21 MHz, and so on.
2) This occurs when you overdrive a CW transmitter, or when you
overmodulate an AM or SSB transmitter. You can fix this by
reducing the drive or microphone gain.
3) You may still have weak harmonics. These can be fixed by
adding a LOW PASS FILTER. A common filter will pass all
frequencies below 30 MHz -- the HF amateur bands -- and
block all frequencies above 30 MHz. So, any harmonics in
the TV frequencies are blocked.
4) This is less of a problem with older transmitters that have
"tuned" final amplifiers. Many modern transceivers require
low-pass filters. Read the owner's manual.
b) Spurious signals (parasitics)
It's also possible for your transmitter to radiate
interfering signals that are NOT harmonics. These are
"spurious" signals, produced in your transmitter, amplified
and transmitted. They can occur at ANY frequency.
1) A common problem is when the power amplifier becomes an
oscillator. This is called "parasitic" oscillation, and is
caused when there is accidental feedback or resonances in
the power amplifier.
2) In the power amplifier, this is fixed by an adjustment
called "neutralization."
3) Parasitics in other circuits can be fixed by shielding and
filtering.
c) PRACTICE QUESTIONS: 2-189, 2-209, 2-213, 2-251.
12. RFI and TVI "miscellaneous"
a) Cross Modulation / Intermodulation
Cross Modulation, or "Intermodulation", occurs when there
are TWO (or more) strong signals on different frequencies.
These signals can "mix" in a rectifier or amplifier to
produce a third frequency...which just might be an
interfering frequency.
1) The clue: this will appear as interference at a specific
frequency.
2) You can fix this by blocking one or both of the problem
frequencies. Since the problem frequencies can be above OR
below the desired frequency, you use a BAND PASS FILTER.
This passes a narrow band of frequencies, and blocks
anything above or below.
3) If that doesn't fix it, the cross modulation may be occuring
OUTSIDE the receiver. Even a corroded metal joint can pick
up and mix radio signals. Your only hope is to find where
this mixing occurs.
b) Key Clicks
This is for CW transmitters only. If you key the RF on and
off instantly, you radiate a broader range of frequencies,
and cause an unpleasant clicking noise in the receiver.
1) Modern transceivers are designed to turn the transmitter
gradually on and off for each dit and dah. (SHOW EXAMPLES
OF WAVESHAPE).
2) Older transmitters can be fixed by putting a capacitor
across the key, and a choke in SERIES with the key leads.
c) PRACTICE QUESTIONS: 2-256, 2-200, 2-186, 2-265.
13. MORSE REVIEW 6: 12345
G. WEEK 4 - MORNING - Transmitters
INSTRUCTOR: Bernie VE3BQM
1. Homework review
2. MORSE LESSON 7: 67890
3. Amplitude Modulation [13]
a) We use radio waves because they travel through the air
without wires.
b) But a radio wave by itself says nothing. It carries no
information. To put voice, or pictures, or bits on a radio
wave, we must change or "modulate" the wave in some fashion.
When we do this, the radio wave is sometimes called the
"carrier" (because it "carries" the information).
c) The simplest modulation is simply to turn it on and off. We
can send Morse code this way. This is called Continuous
Wave modulation, or CW for short.
d) Voice modulation is more complicated.
The human voice is vibrations from 300 to 3000 Hz.
A microphone converts these vibrations to alternating
current. This is called the "audio" signal.
A loudspeaker converts this AC back to vibrations & sound.
1) Note: a loudspeaker can also convert sound to AC, thus
acting as a microphone.
e) So we want to make this "audio" signal modulate a radio
signal. The easist way is to make the audio voltage
increase and decrease the AMPLITUDE of the radio wave.
This is called Amplitude Modulation, or AM.
1) When the radio wave is "100% modulated", its amplitude is
doubled when the audio signal is most positive, and its
amplitude is zero when the audio signal is most negative.
Increasing modulation over 100% causes distortion and
"splatter".
f) An unmodulated radio wave occupies exactly one frequency. A
modulated radio wave occupies a narrow band of frequencies.
These added frequencies are called SIDEBANDS, because they
exist on either side of the "carrier" frequency.
g) With AM, the AUDIO frequency determines the width of the
sidebands. 1000 Hz audio causes sidebands 1000 Hz above and
below the carrier frequency. Human voice (300 to 3000 Hz)
causes sidebands up to 3000 Hz above and below. So the AM
signal occupies a BANDWIDTH of 6000 Hz.
h) All of the "information" in the signal is in the sidebands.
It's possible to send only the sidebands, and not carrier
frequency. This is called Double Sideband Suppressed
Carrier "DSBSC", or just Double Sideband "DSB" modulation.
i) Since one sideband is the mirror image of the other, it's
redundant to send both. If we eliminate the carrier
frequency and one sideband, what's left is called Single
Sideband Suppressed Carrier "SSBSC", or just Single Sideband
"SSB" modulation.
1) One big advantage of SSB is that it occupies half the
bandwidth. You can have two SSB signals in the space
occupied by one AM or DSB signal.
j) PRACTICE QUESTIONS: 2-181, 2-178, 2-179.
4. Frequency Modulation
a) You can also make the audio voltage increase and decrease
the FREQUENCY of the radio wave. This is called Frequency
Modulation, or FM.
1) The amount of the frequency change is called the DEVIATION.
If the deviation is too large -- "overdeviating" -- the
sound will be distorted in the receiver.
2) The sound can also be distored if the transmitter and
receiver are not on the same frequency.
b) Finally, there's a form of "on-off" frequency modulation.
It's called Frequency Shift Keying or FSK. The key changes
the radio wave from one frequency to another. The
difference in the two frequencies is called the "shift".
1) This isn't used for Morse code. It's normally used to send
bits, that is, digital computer data.
2) For digital data, the two frequencies called "mark" &
"space". These correspond to the binary values 1 and 0.
3) The common digital modes are Baudot, ASCII, AMTOR, and
packet.
4) Baudot is what old radioteletypes used. It uses five bits
to represent a character. It is normally sent at 45.5 bits
per second (baud), which yields 60 words per minute. 75 and
100 wpm are also used. The usual frequency shift is 170 Hz.
5) ASCII is what computers use. It uses eight bits to
represent a character.
6) AMTOR is like radioteletype, but with error checking and
automatic retransmission of lost characters.
Mode B is "Broadcast" and is used to call CQ.
Mode A is "Automatic Repeat Request" (ARQ) and is used after
establishing contact.
c) PRACTICE QUESTIONS: 2-183, 3-117, 3-006.
5. CW Transmitter [13]
This is the simplest transmitter. It has six blocks.
a) The POWER SUPPLY provides power to operate the transmitter.
NOTE FOR THE EXAM: this is the ONLY transmitter for which
the power supply is shown.
b) The MASTER OSCILLATOR generates a continuous RF signal of
the desired frequency.
c) The DRIVER/BUFFER amplifies the signal, and isolates the
master oscillator from the power amplifier.
d) The POWER AMPLIFIER amplifies the signal some more, to the
desired final power.
e) The TELEGRAPH KEY turns the two amplifier stages on and off.
This is the CW "modulation". Note that the oscillator is
NOT turned on and off; it must run continuously to produce a
stable frequency.
f) The ANTENNA radiates the signal.
Transmitters always end at the antenna. On the exam, the
antenna is considered part of the transmitter (the last
block.)
g) PRACTICE QUESTIONS: 2-215, 2-137, 2-132, 2-134.
6. BREAK
7. REGS: Input vs Output power
Look at the CW transmitter again.
a) The power supply is providing DC power to the final
amplifier. This is computed from the DC voltage times the
DC current. This is called the "DC input" power.
b) E.g. 2-270. If the "final" is taking 30 mA from a 300 V
supply, the input power is 300 x .030 = 9 watts.
c) The final amplifier takes this DC and converts it to
radio-freqency AC power. This is what gets pumped out to
the antenna. This RF power is called the "output" power.
It can be calculated if we measure the RF voltage, and we
know the load resistance.
d) The EFFICIENCY of an amplifier is the ratio of output/input.
This might range from 30 to 70 percent, depending on the
design of the amplifier.
e) For example, if the input power is 90 watts, and the output
power is 45 watts, the efficiency is 50%.
f) What happens to the "lost" power? It gets turned to heat in
the final amplifier tubes or transistors.
g) PRACTICE QUESTIONS: 2-271, 2-269.
8. Transmitter Building Blocks
The three most important circuits in transmitters and
receivers are oscillators, amplifiers, and mixers.
a) An OSCILLATOR generates an AC signal. Usually this will be
a radio-frequency (RF) signal. It is important that this
frequency be stable; the oscillator should not "drift" in
frequency.
b) An AMPLIFIER makes a signal stronger.
c) A MIXER changes the FREQUENCY of a signal. Actually, it
takes two signals of different frequencies. The output of
the mixer contains the two original frequencies, plus two
new frequencies: the SUM of the original two, and the
DIFFERENCE of the original two.
d) For example, if you put 9 MHz and 5 MHz into a mixer, you
get 9 MHz, 5 MHz, 14 MHz (the sum), and 4 MHz (the
difference) at the output.
e) We will see other building blocks as we look at transmitters
and receivers.
f) PRACTICE QUESTIONS: 2-235.
9. FM Transmitter [13]
The FM transmitter is a little more complicated than the CW
transmitter. It has 7 blocks.
a) The MICROPHONE converts sound to electricity. This is the
"audio" signal.
b) Microphones produce very weak signals, so a SPEECH AMPLIFIER
is used to increase the audio to a usable amplitude.
c) The audio signal is then fed into a MODULATOR. This changes
the frequency of the following stage,
d) the OSCILLATOR. This generates the radio signal. Through
the action of the modulator, the frequency of this radio
signal is varied according to the audio (voice) signal.
e) It's hard to make good VHF oscillators. So the oscillator
works at a lower frequency, and a special circuit called the
FREQUENCY MULTIPLIER increases it to the desired frequency.
Frequency multipliers are simpler than mixers, but they can
only produce harmonics (integer multiples) of the input
frequency.
f) For example, we could have a 28 MHz oscillator, and multiply
it by 5 to get 140 MHz.
g) Like the CW transmitter, the FM transmitter ends with a
POWER AMPLIFIER and an ANTENNA.
h) PRACTICE QUESTIONS: 2-216, 2-140, 2-142, 2-143.
10. SSB Transmitter [13]
The most complicated transmitter is the SSB transmitter.
a) Again there is a MICROPHONE, and a SPEECH AMPLIFIER.
b) Again there is a RADIO FREQUENCY OSCILLATOR which produces
the signal to be modulated. But now this oscillator
produces a fixed and very exact frequency. And now it feeds
into the modulator.
c) The BALANCED MODULATOR uses an audio signal to modulate an
RF signal. It produces a Double Sideband output. That is,
it suppresses the carrier frequency, and lets only the two
sidebands through to the output.
d) The FILTER is a very narrow band-pass filter, designed to
let one of the sidebands through, and block the other
sidebands. Remember, the sidebands are at slightly
different frequencies.
e) At the output of the filter we have an SSB signal at a fixed
frequency, sometimes called the "intermediate frequency."
9 MHz is a common frequency here. To convert this to an SSB
signal in one of the amateur bands, we use a MIXER.
f) The other input to the mixer comes from a VARIABLE FREQUENCY
OSCILLATOR. Since the first input frequency is fixed, this
oscillator will determine the output frequency. For
example, with a 9 MHz IF, if we vary the oscillator from 5
to 5.35 MHz, the sum frequency will vary from 14 to 14.35
MHz. (This is the 20 metre ham band.)
g) Finally, there is a LINEAR AMPLIFIER, and an ANTENNA. The
linear amplifier is a special power amplifier that will not
distort the SSB signal.
h) PRACTICE QUESTIONS: 2-180, 2-123, 2-125, 2-129.
11. MORSE REVIEW 6
H. WEEK 4 - AFTERNOON - Receivers
INSTRUCTOR: Bernie VE3BQM
PROPS: HF rig & antenna
1. DEMO: HF phone & CW operation
2. PRACTICAL: Understanding the HF rig
a) BAND SWITCH selects which HF amateur band to use. That is
it selects the frequency range.
b) TUNING selects the frequency within the band.
c) AF GAIN is the volume control.
So far these controls are similar to any AM/FM radio. Now
for some new ones:
d) MODE selects the type of modulation being received (and
transmitted). Usually the choices are LSB, USB, CW, and
(sometimes) AM. Some rigs have SB-N (normal sideband) and
SB-R (reverse sideband) instead of USB and LSB. You just
have to remember that below 9 MHz, "normal" is LSB.
e) RF GAIN controls the sensitivity of the receiver. Normally
you leave this all the way up. But if there is a strong
signal overloading your receiver, you can turn this down.
f) Some receivers have a PRESELECTOR to help reject signals
outside the ham band. You just tune this for loudest
received signal.
g) OFFSET/RIT (Receiver Incremental Tuning) lets you tune the
receiver to a slightly different frequency than the
transmitter. This is sometimes necessary to make SSB
signals sound right. It's sometimes called "clarifier".
h) Some receivers let you choose different FILTERs. CW
requires less bandwidth than SSB, so if you select a
narrower filter, you'll hear less interference. Remember
that SSB requires about 3 kHz bandwidth. CW filters are
typically 500 Hz or 250 Hz. For AM you need a 6 kHz filter,
and FM can require 25 kHz or more.
i) Many of these controls also apply to the transmitter.
Transmitters also have:
j) CW DRIVE/MIC GAIN controls how strong your CW or SSB signal
is. Sometimes these are two different controls, sometimes
they are combined. This should always be adjusted according
to the owner's manual. Turning DRIVE or MIC GAIN too high
will cause distortion and interference.
k) Older rigs, particularly vacuum tube rigs, have a DRIVER
TUNING control. This is like a preselector for your
transmitter -- you just have to tune it for strongest
transmit signal. If you change frequencies, you have to
re-adjust it.
l) Vacuum tube rigs also have PLATE & LOAD tuning controls.
These adjust a tuned circuit in the transmitter output
stage. Generally you adjust the PLATE control for minimum
plate current, and the LOAD control for maximum output...
but follow the manufacturer's instructions. Like DRIVER
TUNING, you have to readjust these if you change frequencies
(even within the same band).
m) Solid state rigs generally don't require any transmitter
tuning adjustments. Just set the desired frequency, and
transmit.
3. MORSE LESSON 8: .,?
4. Receiver specifications
When you want to know how good a receiver is, you look at
the "three S's": sensitivity, selectivity, and stability.
a) SENSITIVITY is the receiver's ability to pick up weak
signals. Usually this is limited by noise generated within
the receiver. A receiver with more internal noise will be
less sensitive. Sensitivity is measured as the number of
microvolts of signal to produce a given signal-to-noise
ratio.
b) SELECTIVITY is the ability to separate signals close in
frequency. This is determined by the "bandwidth," or how
narrow a slice of frequencies the receiver is actually
hearing. Bandwidth is measured in kHz. A narrow bandwidth
is more selective, but the bandwidth has to be wide enough
for the radio signal. SSB requires about 3 KHz.
c) STABILITY is how well the receiver stays tuned to a certain
frequency. Most receivers will slowly "drift" to a
different frequency. Good ones drift only a few hundred
Hertz per hour.
d) PRACTICE QUESTIONS: 2-219, 2-221, 2-223, 2-225.
5. SSB Receiver [14]
Almost all modern receivers are of the "superheterodyne" or
"superhet" type. These all work by converting the radio
frequency signal to an INTERMEDIATE FREQUENCY, or "IF".
Most of the amplification and filtering takes place at the
intermediate frequency. Here's how it works:
a) The first stage is the ANTENNA. On the exam, this is
considered part of the receiver. So remember that receivers
always begin with the antenna. There may be a tuned circuit
here (the "preselector").
b) Next is the RF AMPLIFIER. This increases the sensitivity of
the receiver, and allows it to hear very weak signals.
Note that the output of this stage is at the same frequency
as the input (the RF frequency).
c) The MIXER converts the radio frequency signal to the
intermediate frequency. Recall that this is done by
"mixing" two frequencies to get their sum and difference.
So, the input of this stage is at the tunable R.F., and the
output is at the fixed I.F.
d) To make a fixed IF from the variable RF, we must add or
subtract another variable frequency. This frequency is
produced by the HIGH FREQUENCY OSCILLATOR, also called the
"local oscillator."
Since this oscillator determines which frequency will be
converted to the IF, this is the tuning control. This also
determines the STABILITY of the receiver.
e) There are several mixer problems on the exam.
1) e.g. 2-240. IF is 9 MHz, receive signal is 13 MHz, what
HFO? (Note that there are TWO possible answers, 4 & 22.)
2) e.g. 2-244. IF is 9 MHz, oscillator is 16 MHz, what RF?
(Again, two possible answers: 7 & 25 MHz.)
3) TWO different radio frequencies will be converted to the
same IF. One is the frequency you want, the other is the
"image" frequency. "Image rejection" is how well the radio
blocks this second frequency.
f) After the mixer, the IF FILTER allows only signals at the
intermediate frequency to pass. This determines the
SELECTIVITY of the receiver.
g) The IF AMPLIFIER amplifies the signal some more. Most of
the amplification occurs here, since it's easy to make a
good amplifier for a single frequency.
Note: on some exam questions, the filter is considered part
of the IF amplifier.
h) SSB signals are converted back to audio by a PRODUCT
DETECTOR. This must replace the carrier frequency that was
suppressed in the transmitter, and demodulate the signal.
i) The carrier frequency is supplied by the BEAT FREQUENCY
OSCILLATOR. Thanks to the mixer, we only have to provide
one frequency here: the Intermediate Frequency.
For example, using a 9 MHz IF, the product detector will
combine a 9 MHz SSB signal with a 9 MHz oscillator to
produce audio.
j) As a bonus, the B.F.O. will "beat" with a CW signal, in the
product detector, producing an audio tone. So this same
receiver works for SSB and CW.
k) The audio signal is not strong enough to drive a loudspeaker
or headphones, so an AUDIO (AF) AMPLIFIER makes it stronger.
There may be a transformer to match the impedance of the
amplifier to the loudspeaker.
l) Finally is the LOUDSPEAKER or HEADPHONES. This is always
the last block on a receiver diagram.
m) PRACTICE QUESTIONS: 2-243, 2-245, 2-232, 2-152.
Be sure to learn the block diagram well.
6. FM Receiver [14]
The first six stages of an FM receiver are IDENTICAL.
The only difference is in how the IF signal is converted to
audio.
a) The LIMITER gets rid of any amplitude variations in the
signal. This is needed by the discriminator.
b) The FREQUENCY DISCRIMINATOR converts frequency modulation to
an audio signal.
c) The AUDIO AMPLIFIER and SPEAKER/HEADPHONES are the same.
So, only two stages are different.
This should make it easier to memorize the receiver block
diagrams.
d) PRACTICE QUESTIONS: 2-236, 2-239, 2-159, 2-162.
7. BREAK
8. Receiver refinements
Before we leave receivers, there are two improvements to the
superheterodyne receiver that may appear on the exam.
a) AUTOMATIC GAIN CONTROL (AGC) keeps strong signals from
blasting your ears. Remember that a local station's radio
signal may be a million times stronger than a distant one!
When a strong signal is received, an AGC signal is fed back
to the RF and IF amplifiers, forcing them to reduce their
gain.
b) DOUBLE CONVERSION solves the problem of image rejection.
Remember that the mixer will accept TWO frequencies to
produce the IF.
Double conversion uses TWO intermediate frequencies, one
after the other. This means two mixers, two local
oscillators, and two IF amplifiers. The first frequency is
chosen for the best image rejection. The second frequency
is chosen for best selectivity.
c) PRACTICE QUESTIONS: 2-247, 2-238, 2-246.
9. REGS: Equivalent Licenses [RIC-25 p.4-5,7-8]
Several different licences allow the use of the amateur
bands. These are listed on the RIC-25 handout, and yes,
there may be an exam question about this.
(READ THE LIST)
10. Repeaters
a) REPEATERS let you cover a wide range on VHF. They do this
by rebroadcasting your signal from a powerful transmitter,
and also receiving and retransmitting the signal of the
other station. They "relay" your signal.
b) Here's the catch: repeaters can't retransmit on the SAME
frequency that you're sending on. So it retransmits on a
slightly different frequency. The difference in the two
frequencies is the OFFSET.
c) On 2 metres, the offset is normally 600 kHz, higher or
lower.
d) So, everyone using the repeater transmits on frequency A.
Everyone listens on frequency B.
The repeater relays signals from frequency A to frequency B.
e) e.g. when you use the Owen Sound repeater, you should send
on 146.340 MHz, and listen on 146.940 MHz.
f) When you give out a repeater frequency, or see a listing in
a repeater guide, you will give out the LISTEN frequency,
and whether the sending-frequency offset is positive (600
kHz higher) or negative (600 kHz lower).
g) e.g., for Owen Sound you would say "146.940 minus". This
says to listen on 146.940 MHz, and to send on a frequency
600 kHz lower than this. (146.340 MHz.)
h) PRACTICE QUESTION: 3-118.
11. MORSE REVIEW 8: .,?
I. WEEK 5 - MORNING - Review
1. Final review
2. MORSE REVIEW
3. Exam advice
a) usually your first impulse is right
b) if you can't work the math backwards, try all the answers
c) if you don't know, guess: no penalty for wrong answers
J. WEEK 5 - AFTERNOON - Exams
EXAMINER: Nick VE3MWU PROCTOR: Brad VE3RHJ
1. Code receiving exam (all students)
2. Written exam 1st shift (2 hours maximum)
3. Written exam 2nd shift (as 1st shift is finished)
4. Code sending exams (as written exams are finished)
K. INDIVIDUAL ASSISTANCE
Rather than cover this during the class presentation, answer these
questions on an individual (one on one) basis, during breaks,
lunchtime, etc.
1. *Buying ham equipment new
a) dealers
b) typical prices
2. *Buying ham equipment used
a) local hams
b) swapmeets
c) swap nets
d) packet listings
e) reference information
f) checking out the rig
g) typical prices
3. *Sources for more information
a) Georgian Bay ARC
$35 to join for 1 year ($30 renewal)
monthly meetings
monthly newsletter
weekly nets (2m, 80m)
special events (e.g. Field Day)
Owen Sound repeater VE3OSR
BITNET Packet BBS VE3IJD
people you can ask for help!
b) Radio Amateurs of Canada
$ per year
our national amateur radio organization
monthly The Canadian Amateur
QSL Bureau
Internet site www.rac.ca